This invention generally relates to apparatus and methods for the manufacture of replacement tissue using tissue engineering methods. More particularly, this invention relates to apparatus and methods for the manufacture of tissue-engineered ligaments suitable for the treatment of ligament deficiencies in patients.
Men and women who are athletically active experience the majority of ligament tears, particularly tearing of the anterior cruciate ligament of the knee. The anterior cruciate ligament is commonly torn by forces applied to the knee during twisting, cutting, deceleration or tackling. A torn anterior cruciate ligament will generally not heal. An anterior cruciate deficient knee is often unstable during pivoting activity. Repeated instability episodes of the knee may lead to further damage of the articular surface and cause tearing in the menisci. It is therefore desirable to stabilize the knee by reconstructing a torn anterior cruciate ligament. Attempts in the past to directly repair the torn anterior cruciate ligaments have been relatively ineffective. Prosthetic ligament replacements made of carbon fibers and Gore-Tex materials do not last a long period of time. Repeated loading of a prosthetic ligament in a young active patient leads to failure of the ligament. The release of debris from a failed ligament results in chronic inflammation of the joint, and osteolysis of bone, in and around the area of ligament attachments.
The current standard practice is to reconstruct a torn anterior cruciate ligament by substituting the torn ligament with a patient""s own tissue. The middle third of the patellar tendon or the hamstring tendons are commonly used as substitution ligaments. Alternatively, the allograft patellar tendon, hamstring tendon or Achilles tendon from a donor can be used for reconstructing the ligament. However, donor materials are associated with a risk of infectious disease transmission such as AIDS. Using a patient""s own tissue is also associated with morbidity at the donor site. For example, stress fracture of the patellar, quadriceps muscle weakness and a long rehabilitation period may result from the use of a patient""s own tissue. Furthermore, harvesting and preparation of autogeneous tissue prolongs surgery time.
Previous attempts to use an artificial stent to replace a damaged anterior cruciate ligament have not been successful. One such example is the LAD Prosthetic Ligament, which was used as a scaffold for tissue ingrowth. The LAD Prosthetic Ligament is not bioabsorbable. Therefore, whatever initial fibrous tissue that forms on the LAD Prosthetic Ligament is not subject to accommodating increasing loads and there is no stimulus for the fibrous tissue to proliferate to support increasing loads. Furthermore, the LAD Prosthetic Ligament is not an optimal structure for tissue ingrowth.
Recent progress in tissue engineering has made it possible to harvest cells from a patient""s own body or a donor. The harvested cells are then grown into the desired tissues on three-dimensional scaffolds, or hydrogel carriers, made of biodegradable polymers. These tissues include, but are not limited to, heart muscles, fat, cartilage, and skin. The tissue grown outside of the body, together with the scaffold containing the tissue, is then transplanted into the patient to correct an existing defect. After transplantation, the cells may further replicate, reorganize and mature, depending on the environment of the host bed into which the cells were transplanted.
Two good sources of cells that are suitable for tissue engineering are embryonic stem cells and mesenchymal stem cells. These stem cells, when exposed to particular bioactive factors, also known as growth factors, can be directed to differentiate into different types of cell lines in a predictable way. For example, mesenchymal stem cells can be directed to differentiate into different types of tissue such as, but not limited to, skin, tendon, ligament and bone under suitable conditions. These conditions include exposing cells to certain growth factors. It is known that mesenchymal cells are directed to differentiate into fibroblast when exposed to interleukin. Furthermore, fibroblast is only able to differentiate into fibrocytes that are the mature cells of ligament tissue.
Mesenchymal cells are present in very small numbers in bone marrow, periosteum, skin and muscle. A small piece of the tissue containing a small number of mesenchymal cells is preferably harvested from the patient""s own body. For example, a piece of periosteal tissue harvested from the patient or donor is morsellised into small pieces. Using tissue culture, techniques well known to those skilled in the art, the mesenchymal cells are isolated and the number of cells expanded. The mesenchymal cells are then seeded onto. scaffolds. These scaffolds are preferably made of biodegradable materials to make the desired tissues.
There are two major challenges in growing tissue-engineered ligaments outside the body. First, most cells cultured in vitro tend to grow in a monolayer. Even if it is possible to culture tissue to a few millimeters thick, deeper layers of the cells may not have sufficient supplies of nutrients. Secondly, it is difficult to adequately and uniformly seed the scaffold with cells to initiate cell expansion.
It is, therefore, an object of the present invention to provide tissue-engineered ligaments for reconstruction of previously torn ligaments.
It is another object of the present invention to provide tissue-engineered ligaments to reduce the time it takes to complete the surgery and to eliminate donor site morbidity in the patient.
It is still another object of the present invention to provide tissue-engineered ligaments grown from a small amount of tissue obtained from the patient.
It is another object of the present invention to provide a scaffold for uniform and adequate seeding of cells to initiate cell expansion for making tissue-engineered ligaments.
It is also another object of the present invention to provide a scaffold for a tissue-engineered ligament with adequate channels for nutrients to reach the cells.
It is also another object of the present invention to provide a method to enhance the growth and alignment of the fibrocytes and the extra cellular matrix during incubation of the tissue-engineered ligament.
Another object of the present invention is to provide tissue-engineered ligaments that will permanently anchor to a patient""s bone.
Yet another object of the present invention is to provide tissue-engineered ligaments that will mature and resist physiological load across the joint.
Still another object of the present invention is to provide a method of making tissue-engineered ligaments.
The present invention comprises an apparatus and method for the reconstruction of a previously torn ligament using a tissue-engineered ligament. The tissue-engineered ligament includes a scaffold of biocompatible material having at least one layer and forming a sheet. The scaffold is placed in a cultured medium for seeding with fibrocyte forming cells. The seeded scaffold is then placed in an incubator to increase the number of cells. The seeded scaffold is then formed into a slender structure suitable for implantation. The method of making a tissue-engineered ligament includes forming a scaffold of biocompatible material having at least one layer forming a sheet. Next, the scaffold sheet is seeded with fibrocyte forming cells. The method further includes increasing the number of cells on the seeded scaffold and forming a slender structure suitable for implantation from the scaffold.